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Do I need a power supply for my guitar pedals?

Updated · By the Suede Social desk

The answer

Yes, once you run two or more pedals. With one pedal, a 9V battery or a single 9V pedal adapter is all you need. If the label says 9V DC, center-negative, get an adapter with those specs and at least the mA the pedal draws. Any supply must match voltage and polarity. Extra mA is fine.

Read the label first

Every pedal lists its power needs next to the power jack, on the underside, or in the manual. Here is what each part means.

9V DC
The voltage, and the kind of power: DC means direct current. Most compact pedals run on 9V DC. Some take 12V, 18V or AC power, and those need an output that matches.
The polarity symbol
A small diagram of a dot inside a C shape, with a plus and a minus sign. If the minus sign connects to the center dot, the pedal is center-negative, the most common setup.
mA
Milliamps: the current the pedal draws. The supply output you plug it into must offer at least that much.

Pick the right supply in six steps

  1. 01Read every labelWrite down the voltage, polarity and mA for each pedal. It costs nothing and answers most power questions before you spend a cent. No mA figure on the pedal? Check the manual, the maker’s site, or the pedal power database.
  2. 02Flag the odd ones outMost compact pedals take 9V DC, center-negative, through a standard 2.1mm barrel plug. Mark any pedal that differs: 12V or 18V, AC power, center-positive, positive ground, or a different plug size. Those need a matching output, a polarity-reversing cable or a plug adapter. Positive-ground fuzz pedals, including many germanium designs, need a battery or an isolated output: on a shared daisy chain they can short the supply. Run a pedal above its rated voltage only when its maker says it supports that voltage.
  3. 03Add up the mATotal the mA of every pedal. A supply or output rated for more current than the pedal draws is fine, because a pedal only pulls the current it needs. One rated for less runs short, and pedals can cut out, reset or refuse to start.
  4. 04Choose daisy chain or isolatedA daisy chain runs several pedals from one adapter and suits a small board. An isolated supply gives every pedal its own separate output. A digital pedal on a daisy chain can add hum or whine; if it does, give it an isolated output.
  5. 05Match each pedal to an outputEvery output on a multi-output supply has its own mA rating, printed on the unit or in its manual. Put the hungriest pedals on the strongest outputs, and set any switchable outputs to the voltage each pedal needs. The power planner checks the fit for you.
  6. 06Leave a spare outputBoards grow. An empty output or two today saves buying a second supply when the next pedal arrives.

Isolated vs daisy chain

Daisy chain
One adapter and one cable with several plugs. Every pedal shares the same supply and the same ground. Cheap and tidy for a small board. A digital pedal on a shared chain can add hum or a high whine; if it does, give it an isolated output.
Isolated supply
Each output is electrically separate from the others, so noise from one pedal stays out of the next. It costs more and runs quiet, and many models offer outputs at more than one voltage.

The working rule: a daisy chain from a pedal adapter with enough mA for every pedal on it is a fine start for a small board, digital pedals included. If one pedal adds hum or whine, move that pedal to an isolated output. Once the board outgrows one adapter, move to an isolated supply.

What about batteries?

A 9V battery works well in a low-draw analog pedal and keeps a single pedal free of power cables. Many digital pedals have no battery slot, so they run on an adapter. On many pedals that take a battery, the input jack is the power switch, so a cable left in the input keeps draining it. Unplug the input when you stop playing, and change the battery as soon as the pedal sounds thin or starts to sputter.

Common mistakes

  • Using an adapter from another gadget because the plug fits. It can be the wrong voltage, AC instead of DC, the wrong polarity, or noisy. Use a supply built for pedals.
  • Ignoring the polarity symbol. Center-positive power on a center-negative pedal can damage it.
  • Blaming a digital pedal for hum before checking its power. On a daisy chain it can add hum or whine; if it does, give it an isolated output.
  • Running a positive-ground fuzz off a shared daisy chain through a polarity-reversing cable. It can short the supply. Use a battery or an isolated output.
  • Buying the supply before counting the pedals. Count outputs, mA and voltages first.
  • Worrying that a supply with more mA will hurt a pedal. It will not. Voltage and polarity are what you match.

Words used here

Voltage (V)
The electrical pressure a pedal is designed for. Match it exactly unless the maker lists a range.
Current (mA)
How much current a pedal draws, in milliamps (thousandths of an amp). The supply must offer at least that much.
Polarity
Which part of the plug is positive and which is negative. Most pedals are center-negative.
Positive ground
An older circuit layout, common in germanium fuzz, that uses the positive side as ground. It needs a battery or its own isolated output.
DC
Direct current, the steady kind of power most pedals use. A few pedals run on AC and need an AC supply.
Daisy chain
One adapter feeding several pedals through a single cable with several plugs.
Isolated output
A supply output that is electrically separate from the others, which keeps noise from passing between pedals.

Tools for this

First Year · the forum

Still stuck? Ask the room.

Post in First Year with the suggested title and a fill-in template already in the post.

Make it easy to answer: List every pedal with the voltage and mA from its label, and say how many more pedals you plan to add.

Suggested title: “Which power supply should I get for my pedals?”

Ask in First Year

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